Interpolation is a technique for approximating the value of a curve or waveform between points for which samples of the curve or waveform are available. Application of the technique may require subtracting a higher-index sample value from a lower-index sample value. Because any individual sample may be either the higher-index sample or the lower-index sample value depending on the particular point to be interpolated, in applications where real-time processing speed is important, double storage of all samples may be needed to avoid time-consuming reordering of the samples or negation of a negative difference.